Loud speaker



June 19, 1928.

F. O. FARWELL LOUD SPEAKER Filed May 25, 1927 5 Sheets-sheaf 1 June 19, 1928. 1,674,323

F. O. FARWELL LOUD SPEAKER Filed May 23, 1927 s Sheets-Sheet 2 June 19, 1928 F. O. FARWELL LOUD SPEAKER Filed May 23, 1927 3 Sheets-Sheet Patented June 39, 1%28.

FAY 0. FARWELL,

or TOLEDO, orno.

LOUD SPEAKER.

Application filed May 23,

My invention has for its object to provide a means for efficientlyamplifying sound vibrations. The sound vibrations may be produced electromagnetic'ally' in one or more a members, each of which is so constructed that it will reproduce with greater facility a certain part of the scale, one being particularly efiicicnt for translating electric vibrations into sound located in one part of the In scale, and the other, or others, of the members being particularly adapted for translation of sound in another part, or other parts, of the scale and so that the parts of the scale that are more efiiciently translated will cover 15 the entire scale, each of the translating devices, however, being capable of translating electric vibrations into sound. throughout the entire scale whereby the entire scale will be most efficiently translated by the translating devices. I I

The invention also provides a loud speaker that is so constructedas to megaphonically reproduce the'sound produced in the mem-- bers of the characteristically different translating devices. A inegaphonic means is associatcd with each of the translating means;

and is so constructed as to most 'el'licientlymagnify sound of the particular translating means with which it is associated, although it will magnify the sound of all parts of the scale that is produced by the translating means with which it is. associated. Each megaphonic means-is also adapted to produce a characteristic tone quality which is distinctly pleasing and so that both lower and higher tone qualities may be produced in the same loud speaker. The combined effect of the translating means and the megaphonic n e/ans is'an exceedingly harmonious, accurate and a uniform reproduction of the elec-' tric sound of the entire tone range. The invention also provides'a means. for selectin a particular set of associated parts of the loud speaker for reproduction of.sound that may 7 be electrically transmitted .to the instrument, and, consequently, the desired tone quality and definiteness of articulation may be selected as may be desired. Thus, where the sound is more or less limited to certain-rates of vibrations. as when a piccolo is playing, one of the of instrumentalities' may be used to the exclusion of the other, or-others, likewise when a cello is played the sound thercof is electrically transmitted and another set 55 of associated parts of the loud speaker may be utilized. 'Or, as stated above, all of the 1927. Serial No. 193,955.

ings.

- The invention'maybe contained in struc-' tures of different forms and to illustrate a partichla'r application of the invention, I have selected a loud speaker containing the invention as an example of such structures and shall describe it hereinafter. The particular structure selected for purposes of illustration, is shown. in the accompanying drawings.

Fig. 1 is a front view of the loud speaker selected as an'example. Fig. 2 is a rear view of the speaker. Fig. 3 is a side view of the speaker shownin Figs. 1 and 2. Fig. 4 illustrates a view of a section of the loud speaker. Fig. 5 illustrates an end view of the compound unit for translating the vibratory electric currents into sound waves. Fig. 6 is a view of a section taken on the plane of the line 66 indicated in Fig. 5.

ig. 7 is a view of a section taken on the plane .of the line 7''( indicated in Fig. 6. Fig. 8 is a view of a section taken on the plane of the line'8-8 indicated in Fig. 6. Fig. 9 is a view of a section taken on the lane of the line 9- -9 indicated in Fig. 6.

ig. 1O is a diagram of the connections.

that may be made betweenthe translating devices and an external circuit whereby one or more. of the translating devices'may be connected for transforming the electric vibratory currents into sound waves.

The loud speaker 1, of the drawings, is,

provided with a supporting base 2 and a pedestal 3, the instrumentalities of, the loud speaker including the translating devices and the megaphonic means are supported in a circularshell 4 that is formed substantially in the shape of a central section of a sphere. by a plate 5 in the form of a frustum to which a handle 6 may be secured for carrying and handling the 'loud s eaker.- The smaller end of the frustumal p ate 5 may be closed by a suitable screen 7. The front of the shell may be closed by a. suitable cone 105' The rear end of the shell is. plosed ire into the corresponding sound vibrations.

Each translating means will, however, cause a vibrating member to respond to all of the vibrations transmitted and produce sound in all of the parts of the scale and in unison with the movements produced in thevibra- .tory member of the otlier translating means and so that a harmonious result will be produced in whatever part'of the scale the sound' is located in. The electromagnetic unit has therefore translating nstrumentalities that operate independently of each other and yet cooperate in unison so that all of the translating devices will produce sound.

The compound electromagnetic unit 10 shown in the drawings is supported in operative relation to "the megaphonic devices of the loudspeaker. A mega: phone in the form of 'the curved horn 11 is ,secured to and st pported in the shell 4. The horn llhis tapered in form, its smaller end being connected to the electromagnetic unit 510 and its large open end 12 terminating in closeproximitylo the smaller end 13. The horn 11 is connected to the shell and supported b-y -means of a bracket 14 that is connected tothesinaller end of the horn l1 and to the frushm'ial metal sheet The smaller end is turned substantially at right angles to the plane'of the center jline of the born as at 15, and is connected to the electromagnetic unit 10. If desired the interior of the smaller end of the horn may be threaded and the electromagnetic unit may be provided with the thcaded boss 16. Thus the two parts may be connected together by rotating one relative to the other with the threads of the parts-interfitting. The elec tromagnetie unit lfl is thus supported substantially at the axis of the shcll ,of the loud speaker. p

The electromagnetic unit 10 is provided with a permanent magnet 20 and a. pair of pole pieces 21 extend inwardly from the ends of. the permanent magnet :20 and terminate in the cores 22 on which the coils" 23 are 'located. Thus the cores 22 are polarized and the current-through the coils 23 operate' to vary the field'of force existingbctwoenthe free ends of the cores.

cores are located in juxtaposed relation to thediaphragm 24' of magnetic material. The diaphragm 24 is secured in close proximity to the opening 25 thatisformed in thc lrOsi The electromagnetic unit is a The free ends of the 16 which is connected to the smaller end of the megaphoneor born 11. The coils 23 opcrate to set up vibrations in the diaphragm 24 and the horn magnifies the sound that is thus electromagnetically translated from the vibrations of the electric current that passes through the coils 23. The diaphragm 24 is in the form of a disk and covers a recess 26 of large-diameter.. The diameter of the recess 26,is considerably larger than the diameter of the opening 25 in order'to confine a large amount of air which is caused to pu1- sate through the opening and thus cause vibration of the column of air within the horn 11 and also of the horn itself. The horn also receives vibrations from the (ha phragm through the plate 27 to which the horn is connected in the manner well known in the art. i

The translating device, comprising the polarized cores 22, the coils 23 located on the cores, the diaphragm 24 which is clamped between the plates 27 and 28, operate to translate the electric vibrations into sound vibrationsot' all parts of the scale but which is, by reason of its construction, particularly efficient for translating the electric vibrations into sound having the higher rates of vibration. The horn is particularly adapted to magnify all rates of vibrations of sound that 95 are produced by the diaphragm but is par-\ ticularly cflicicnt in amplifying the higher rates of vibration and produces a characteristic and pleasing tone quality. Furthermore its quality is such as to produce the sharper sounds that is, it produces distinctive sounds that terminate and begin sharply, or, it articulates accurately, to use a phrase commonly used in connection with speech.

The permanent magnet 20 is also provided 1 with thepole pieces 30 that extend inwardly with respect to the ends of the permanent magnetand are turned at right angles to form the polarized cores 31. The coils 32/ are located on the cores 31 and operate to 11" vary the magnetic field between the outer ends of the cores 31. The pole pieces 21. are, preferably, so located that the coils 32 may be located between the ends of the permanent magnet 20. The ends of the cores 31 ex-- extend inwardly with respect to the permanent magnet, but are also inclined towards the center of the magnet, that is, in the par ticular form shown, towards the curved part of the magnet. This disposes the coils 23 in close proximity to the cores 3Land between the coils 32 and the curved part of the perfmanent magnet.

1. The ends of the cores 31 are in close proximity to a bar 35 of magnetic material.

in the form of construction shown in the 139 imity drawing, the cores are located in close proxto the central part of the bar 35. The bar 35 may be formed of sheet metal and stiffened by turned up edge portions of the sheet metal as at 36. The turned up edge portions extend trom one end. of the bar where it is secured by means'of the threaded rod 37 to near the opposite end portion where it is secured in position by a pair of threaded rods 38 that extend 'through ears 39 formed on the end of the bar. The bar is secured in position by means of nuts 40 located on the threaded rods 37 and 38. Thus the bar flexes in the portion 41 located between the ears 39 and the ends of the'turned up edge portions 36. The bar has considerable length and is operated on centrally and consequently to maintain such resiliency that it will respond to the changes of the field produced by the coils 32, the central part'of the bar is stiffened and having end portions that are suiiiciently elastic to permit vibratory movement of the central portion that is thus stifl'ened. This produces. comparatively a structure which, however, is bodily vibrated by the change of flux in the magnetic field produced by the coils 32 in their action on the polarized cores 31. It also afi'ords a means whereby accurate adjustment may be made relative to the cores so as to maintain the armature in a floating relation with respect to the cores and prevent freezing-of the armature on the cores. The adjustment is obtained by means of the rod 37 to locate the armature in the more intense field while its peculiar construction prevents freezing contact notwithstanding its length. The rods 38 are secured to the plate 28 while the rod 37 extends through theplate 28 andhas a threaded end 45. An adjusting rod 46 is threaded onto the end of the rod 37 and a sprin 47 is located intermediate the plate 28 and the nut 48. The adjustment of the bar relative to the cores 31 is brought about by rotation of the adjusting rod 46.

In order to increase the mass of the magnetic material in proximity to the ends of the cores 31, a piece of soft iron 50 may be welded to or secured to the central portion of the bar 35. The soft iron part operates as an armature for the ends of the cores 31. It extends across the ends of the core and the bar is adjusted so as to locate the part 50 in the desired effective relation to the ends of the cores. The magnetic part 50 is placed in closer proximity to the ends of the cores 31 by rotation of the adjusting rod 46 in one direction. It the rod 46 is r0- tated in the opposite direction the spring 47 will operate by reason of its elasticity to move one end of the bar 35 in the opposite direction so as to move the magnetic part 50 further from the ends of the cores 31.

The cores 22 are adjusted relative to the The cone of thin,

' vibrations.

diaphragm 24 by means of a bar of diamagnetic material 55 which has turned edge portions 56 to stiffen the bar 55. The bar 55, which may be formed-of brass, is connected to pole pieces 21, the bar being provided with a pair of cars 56 that project at an angle to the .center line of the bar 55 and so as to extend in the direction of the pole pieces 21. It is secured by means of screws 57 to the polepieces 21. The other end of the bar 55 is'secured to the end of the rod 58. Theend of the rod 58 is riveted to the bar 55. The lower end of the bar 58 .is

threaded and aspring 59 is located intermediate a nut 60 located on the rod 58 and. The rod 58 extends through the plate 28. j the plate 28 and an adjusting rod 61 is threaded-onto the end of the rod 58. Rotation of the adjusting rod 61 draws the end of the rod 55 downward and in so doing flexes the pole pieces 21 and moves the cores 22 and the coils 23 towards the diaphragm 24. Rotating the adjusting rod 61 in the opposite direction permits the elasticity of the springs 59 and of the pole pieces 21 to operate and raise the rod 55 and move the ends of the cores 22 away from the diaphragm 24. The adjusting rods 46 and 61 extend through the screen 7 and handles 64 and 65 are connected to the outer ends of the adjusting rods 46 and 61 whereby the adjustments of ,the translating devices may be readily made.

8. is supported on the armature 35 by means of a rod 70. The rod isconnected to a thimlo'le or block 71 that is secured to the bar 35 and to a collar 72 that is secured to the apex of the cone 8. The collar 72 may be provided with a set screw 73 for adjustably locating the cone 8 on the rod 70 to adjust the cone 8' to the edge of the shell 4 of the 10 d speaker. The cone 8' of flexible materi 1 15 particularly adapted to 'megaphonicitlly reproduce the vibrations set up by the translating means, comprising the polarized colres 31, the coils-.32. and the'bar 35, will transform the vibrator currents that pass through the coils 32 into sound This translating .means, however, is particularly efiicient in producing the lower notes of the sound that is electrically transmitted. to the compound magnetic unit 10 and the cone 8 of flexible material is particularly eflicient in amplifying the sound of the lower notes of the scale and producing a characteristic pleasing tone quality. Frequently reproducing elements will have characteristic modulations or tone qualities when reproducing sound other than that for which they are particularly adjusted or constructed that are not as pleasing to some individuals as other tone qualities. In the compound electromagnetic unit of the construction embodying my invention, ,these light, flexible material qualities that may not be so desirable will be overcome or caused to be submerged by the action ofthe instrumentalities that are working more pronouncably. 'Thus sound modulated by the particular characteristics of the translating devices and its associated megaphonic means, does not appear in the reproduction of the sound produced by the speaker as a whole. The parts, however, willcoa-ct harmoniously to reproduce the sound and consequently they cooperate to elliciently translate and amplify the sound transmitted through the electric connections to the coils of the electromagnetic unit.

In the constructionembodying my invention, either set of coils may be connected with the external circuit and the other set of coils may be disconnected, or both sets of coils may be connected to the external circuit,

whereby the desired tone quality may be produced which is most pleasing to the lisher. The external circuit may be connected to "either set of coils or to both sets by means of a suitable switch 75 as indicated 2 in'the diagram illustrated in Fig. 10. The

circuits of the coils 23 and 32 are connected to pairs of fixed contacts 76 and 77 and the switch 75 is provided with the rotatable contacts 78 and 79, which are connected to the externalcircuit 80. The contact 78 is adapted to connect with both contacts 7 6 and 77 or with contact 76 or 77 of each pair. Likewise contact 79 is adapted to connect with the other contacts 76 and 77 or with a contact 76 or contact 7 7 of each pair. lVhere the contacts 78 and 79 are located in contact with the contacts 76, the coils 23 will alone be connected with the external. circuit 80 and where the contacts 78 and 79 make conct with the contact 77, the coils 32 alone 11 be connected in the circuit 80 and where the contacts78 and 79 connect with both pairs of contacts 76 and 77, the coils 23 and 32 will be connected in parallel in the circuit 80. Thus the sound may be reproduced b either set of translating means and megaplionic means or by both sets in order to obtain the desired results, If, therefore, an instrument is playing wherein high notes are sounded quite entirely, the translatingmeans and the megaphonie means associated with the coils 23 may be brought into action. Also, where low notes are largely being transmitted, it may be found desirable to Bring into action the coils 32 and the associated megaphonic means, but where an orchestra is being played, that is, where the tones will extend over the entire range of sound production, it may be found desirable to connect both sets of coils with the external circuit. 1

I claim:

.1. In a loud speaker, a compound unit having 'partsfor translating sound waves of tlififerenttone qualities, one of the said diaphragm in operative position with re-' spect to the air column of the horn, an electromagnet for vibrating the diaphragm, a flexible cone covering one side of the car'- ing, an armature secured to the flexible cone,

and anclcctromagnet for vibrating the ar-.

mature. 1

3. In a loud speaker, a permanent magnet, a' pole piece secured to each pole of the permanent magnet, said pole pieces converging to a. point between the legs of the magnet and terminating to one side of the magnet, electromagnetic coils surrounding each pole piece, a magnetdiaphragm forming an armature positioned in spaced relation to the pole pieces to form an air gap between the armature and the pole pieces, means for adjusting the air gap between the diaphragm illl'l'l-tltllle and the pole pieces, 7

an external circuit connected to the coils, a

horn associated with the diaphragm to amplit'y sound waves produced by the diaphragm, a second-pair of pole pieces secured to the legs of the magnet opposite the first named pole pieces and converging between the legs of the magnetand located parallel to the first named pole pieces, crectromagnet coils associated with each of the last named pole pieces, an armature positioned in spaced relation to. the last named 'pole pieces, so that there is an.v air gap between the armature and the pole pieces, means for adjusting the air gap between the last named pole pieces and the armature and an amplifying means secured to the 'armature to amplify the sound waves pro duced by the armature. v

4;. Ina loud speaker, a permanent-magnot, two pole pieces converging, from and operatively connected to each'pole of the magnet one pair of pole pieces terminating on one side of the magnet, the other pair of pole pieces terminating toward the other side oi the magnet, an armature adjustably positioned in relation to one pair of pole pieces, an armature forming diaphragm adjustably positioned in relation to the other pair oi pole pieces, electromagnetic coils as socia'ted with the pole pieces adapted to vary the magnet influence of the pole pieces on the armature and on the diaphragm to cause the armature and the diaphragm to vibrate, and means to amplify the vibration coils located on the said pole pieces, a metal diaphragm located in operative relation 'to' of the armature and the diaphragm into audible sound waves.

5. In a loud speaker, a compound magnetic unit comprising a U-shaped perma ncnt magnet, two pairs of pole pieces secured to the poles of the magnet and protruding from opposite sides of the magnet, coils located on the said polepieces, a metal diaphragm located in operative relation to one pair of the pole pieces, an armature formed of sheet metal located inoperative relation to the other pair of pole pieces, a horn located in operative relation with respect to the metal diaphragm and a" flexible diaphragm mechanically connected to the armature.

6. In a loud speaker, a compound magnetic unit comprising a U-shaped perma-- nent magnet, two pairs of pole pieces secured to the poles of the magnet and protruding from opposite sides of the magnet,

one pair of the pole pieces, an armature formed of sheet metal located in operative relation to the other pair of pole pieces and having a raised portion to stiffen a partof the said armature, a horn for sup orting the compound unit,and located in operative relation to the said metallic diaphragm, a

shell for containing, the said horn, and a flexible diaphragm forming one side of the said shell. 1

7- In a loud speaker, a compound magnetic unit comprising a U-shaped permanent magnet, two pairs of pole pieces securedto the poles of the magnet and prot-ruding' from opposite sides of the magnet, coils located on the said pole pieces, a metal diaphragm located in operative relation to one pair of the pole pieces, an armature formed of sheet metal located in operative relation to the other pair of pole pieces and having a raised-portion to stiffen a part. of the said and the metallic diaphragm relative to their associated pole pieces. In Witness whereof I have hereunto signed my name to this specification.-

FAY O. FARWELL. 

